1 00:00:00,200 --> 00:00:07,820 So Ethernet has been a relatively inexpensive, reasonably fast and very popular LAN technology for, 2 00:00:07,910 --> 00:00:09,420 gosh, several decades. 3 00:00:09,440 --> 00:00:17,810 It was commercially introduced in 1980 and first standardized in 1983 as I triple E 802.3. 4 00:00:18,460 --> 00:00:24,670 And has since been refined to support higher bit rates and longer link distances. 5 00:00:25,940 --> 00:00:31,220 Ethernet has since become the most popular and probably the most widely deployed network technology 6 00:00:31,220 --> 00:00:32,390 in the world. 7 00:00:32,659 --> 00:00:39,020 Many of the issues involved with Ethernet are common to many network technologies and understanding 8 00:00:39,020 --> 00:00:45,830 how Ethernet addresses these issues can build a foundation that will improve your understanding of networking 9 00:00:45,830 --> 00:00:46,700 in general. 10 00:00:48,240 --> 00:00:52,530 So let's keep the design principles of Ethernet simple. 11 00:00:53,490 --> 00:01:01,440 The basic idea of its design is that multiple computers have access to it and can send data at any time. 12 00:01:01,940 --> 00:01:06,550 If two computers send data at the same time, a collision will occur. 13 00:01:06,560 --> 00:01:11,480 So and when this happens, the data set is is not going to be usable. 14 00:01:12,030 --> 00:01:19,230 In general, both computers will stop sending and wait a random amount of time before they'll try again. 15 00:01:19,620 --> 00:01:23,490 Now a special protocol was developed to deal with such problems. 16 00:01:23,490 --> 00:01:29,430 It's called Carrier sense Multiple access with collision detection. 17 00:01:29,700 --> 00:01:32,790 Or it might be easier to say Csma CD. 18 00:01:34,200 --> 00:01:39,270 Today, Ethernet cables look like, well, thick telephone cables. 19 00:01:39,390 --> 00:01:45,840 Modern cables connect to hubs or switches, and each cable runs from a computer's network interface 20 00:01:45,840 --> 00:01:49,230 card, the Nic to such a box. 21 00:01:49,590 --> 00:01:57,180 Now, here are the most widely known Ethernet cables ten base two and ten base five cables are what 22 00:01:57,180 --> 00:01:59,840 I would call retro coaxial cables. 23 00:01:59,850 --> 00:02:01,860 You don't see them much today. 24 00:02:02,400 --> 00:02:09,240 Each computer has a T plugged into it and cables plug into each side of that t. 25 00:02:10,590 --> 00:02:20,550 Ten base t 100 base t 1000 base t are all unshielded twisted pair or UTP cables, which look a lot like 26 00:02:20,550 --> 00:02:25,800 thick phone cables, and they go from each computer to a hub or a switch. 27 00:02:26,460 --> 00:02:32,880 Initial numbers indicate the supported speed so that ten will stand for ten megabits per second, and 28 00:02:32,880 --> 00:02:38,490 1000 stands for 1000 megabits, also known as gigabit or one gigabit. 29 00:02:40,200 --> 00:02:48,930 In base F cables are the same as ten base T, but they are fiber cables and they'll transmit light pulses 30 00:02:48,930 --> 00:02:52,170 instead of electrical signals over copper. 31 00:02:53,690 --> 00:03:00,350 A data packet on an Ethernet link is called an Ethernet packet, which transports an Ethernet frame 32 00:03:00,350 --> 00:03:01,610 as its payload. 33 00:03:02,320 --> 00:03:11,770 An Ethernet frame is preceded by a preamble and start frame Delimiter or SFD, which are both part of 34 00:03:11,770 --> 00:03:14,920 the Ethernet packet at the physical layer. 35 00:03:15,310 --> 00:03:15,820 Right. 36 00:03:16,460 --> 00:03:18,590 There are four types of Ethernet frames. 37 00:03:19,120 --> 00:03:25,030 And the most common one is the Ethernet to frame, also known as Dic's frame. 38 00:03:25,940 --> 00:03:28,790 We're talking about the Ethernet two frame at the moment. 39 00:03:30,230 --> 00:03:32,450 Each Ethernet frame starts with. 40 00:03:33,560 --> 00:03:40,880 An Ethernet header which contains destination and source Mac addresses as its first two fields. 41 00:03:41,700 --> 00:03:48,090 The middle section of the frame is payload data, including any headers for other protocols. 42 00:03:48,090 --> 00:03:52,140 For example, internet protocol carried in the frame. 43 00:03:53,240 --> 00:04:02,270 The frame ends with a frame check sequence or FCS, which is a 32 bit cyclic redundancy check used to 44 00:04:02,270 --> 00:04:05,270 detect any in-transit corruption of data.